Memnarchitect is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Spells you cast have affinity for artifact creatures that weren't originally artifact creatures. (They cost less to cast for each artifact creature you control that wasn't originally an artifact creature.) : Target permanent becomes an artifact in addition to its other types.